Shown in FIG. 2 is a conventional photoelectric coordinate sensing panel of this type. Namely, in FIG. 2, printed circuit boards 1a and 1b are light emitting element substrates and boards 2a and 2b are light sensing element substrates. The light emitting element substrates 1a, 1b and light sensing element substrates 2a, 2b are respectively arranged across from each other on the X and Y axes to form a rectangular frame.
The light emitting element substrates 1a, 1b are provided with a plurality of light emitting elements (LEDs) 3 in a line or in a curve fitting to the curvilinear surface of a display in view of alleviating parallax, while the light sensing element substrates 2a, 2b are provided with a plurality of opposing light sensing elements 4 also in a line or in a curve fitting to the curvilinear surface of a display. A switching circuit 5 is also provided on the boards.
In this photoelectric panel the light from LEDs 3 transversely crosses near the surface of display forming a lattice of infrared beams 6 and unique addresses are assigned to each photoelectric element along an axis (X or Y). By sequentially accessing each photoelectric detector, it can be determined which LED 3 emits the light and which light sensing element 4 senses the light by switching the control lines connected to the LEDs 3. When a displayed image on the display screen is touched with a finger or a touch pen, the infrared beams 6 are interrupted, the X-Y coordinates of the interrupted infrared beams 6 are sent to a computer. When a wide object (finger) also blocks the infrared beams 6 of a plurality of rows and columns adjacent to the center position, the intended center point can be obtained by averaging the data. Various measures are taken for invalid interruptions using logic circuits and disturbance of the light beam are compensated by a compensating circuit.
However, in such a photoelectric touch panel, where a circuit needs to be formed on each substrate and assembled into the form of a frame, the wiring becomes complicated, making assembly troublesome and preventing reduction in size.
Recently, as shown in FIG. 3, there was developed a touch panel in which the light emitting elements (LEDs) 8 and light sensing elements (photo-transistors) 9 are provided in parallel along sides of a shielding plate 10 on the same substrate 7a (7b) in the periphery of the display 13, and a reflector 11 such as a mirror is provided to the substrates 7c, 7d opposing the substrates 7a, 7b and the light beams 12 are formed like a lattice through reflection of light emitted from the LEDs 8.
However, in the photoelectric touch panel of this type, the distance which a light beam travels until it reaches the phototransistor 9 is doubled and thus a greater portion of the light is dispersed or scattered before reaching the photo transistor 9.